Electrical fence charging apparatus



May 8, 1945. N. F. AGNEW T AL, 2,375,458

ELECTRICAL FENCE CHARGING APPARATUS Original' Filed Sept. 6, 1959 Ild Z2 l u I. la'.

INVENTORS Meg/@Myer Ngazgd THEIR A ORNEY Patented May 8, 1945 UNITED STATES lPATENT oFFICE v 2,375,458 v ELECTRICAL FENCE CHARGING APPARATUS Norman F. Agnew and Willard P. Place,

Wilkinsbnrg, Pa.

Original application September 6, 1939, Serial No. 293,582. Divided and this application March 17, 1943, Serial No. 479,418 g closing conductor or fence for the purpose of keeping farm stock from straying beyond the enclosure. In such installations, it is usual to impress the charging potential between one or more of the enclosing conductors and ground so that an animal coming in contact with the conductor Will complete a discharge circuit to ground. Since the fence charging apparatus, to be safe, must incorporate certain current limiting features, it is apparent that the presence of an appreciable leakage current from the fence to ground such as may be caused by weed growths touching the charged conductor will impair the eiectiveness of the stock enclosure. 'This problem is particularly acute in the case of an electric fence several miles long passing over uncultivated land or over moist ground where vegetation growth may be abundant. Diiliculty is also encountered in the case of a low fence close to the ground, such as s required for herding small farm stock.

One object of apparatus embodying our invention is to render such an electric fence automatically self-cleaning with respect to vegetation coming in contact therewith, thus avoiding the necessity for frequent periodic inspection of the fence and manual cutting of the weed growth.

Another object of the apparatus embodying our invention is to prevent the growth of vegetation and advantages will appear as the description pro- The present application is a division of our copending application Serial No. 293,582 flied on Seltember 6, 1939, for Electrical fence charging appel-anis.

We shall describe several forms of apparatus embodying our invention and shall then point out the novel features thereof in claims.

In thev accompanying drawing, Fig. 1 is a diagrammatic view showing one form of apparatus for preventing short-circuits by vegetation embodying our invention. Figs.-2', 3, and 4 are diagrammatic views showing modied forms of the apparatus of Fig. 1, also embodying our invention. Fig. 3 shows, in addition, apparatus embodying our invention for providing an alarm when contact is established with the charged conductor.

' Figs. 1a to 4a, inclusive, show diagrammatically the lform of the voltage or current output of the apparatus shown in Figs. 1 to 4, inclusive.

Similar reference characters refer to similar parts in each of the several views.

We have discovered in the course of practical operation of apparatus embodying our invention that within the range of voltages such as are safe for the purpose of fence charging, the polarity of the potential on the charged conductor plays an extremely important partv in determining the winding Il, over the contact inger I3 of the vi-A efi'ectiveness oi the apparatus in keeping the fence clear of weeds. We have lfound, for example, that if the charged conductor is made positive, as indicated by a voltmeter or a milliammeter connected between the conductor and ground, then the apparatus is highl'y eiective even at relatively lowsvalues of discharge current, andeven if the potential is not applied'const'antly but is applied A impulse current such as canbe considered safe for fence charging purposes. Accordingly, our invention includes as one of its important features the placing of a positive charge upon the conductor and supplying the conductor with a substantially unidirectional potential.

Referring now to Fig. l, the apparatus of this' figure is energized from a source of direct current B and a vibrator V having rectifying contacts is used for obtaining the necessary unidirectional potential for charging the enclosing conductor or fence I0. .The primary windingll of thestep-up transformer TI has a mid-tap to which is connected one terminal of the battery B, the other terminal o! the battery being connected alternately. rst to one hall, and then to the other half of tube DTi.

-contacts of the vibrator.

brator V. This vibrator may be of any suitable and well-known design and as shown, is constantly energized from the battery B over an obvious circuit which includes the lower half of winding II, In operation, the contact finger I3 alternately causes the flux in the core of the transformer TI to reverse at a relatively rapid rate by virtue of the alternate energization in opposite directions of the two halves of the 'primary winding, thus causing an alternating output voltage of substantial magnitude to be induced in the secondary winding I2.

The output from the transformer Ti is rectiiled over a second contact finger I4 of the vibrator and is impressed across the conductors 8 and 9. The polarity is so selected that the charge on wire 8 is positive with respect to wire 9 which is connectedto ground at G. Wire 8 is connected with the charged conductor Ill through a protective resistor R and also through a second resistor R2 around which is connected the discharge The resistor R2 has a relatively low ohmic value as compared with resistor R, its resistance being sufficient merely to provide a potential drop adequate to cause the tube DTI to glow in the event that conductor I becomes grounded. By connecting the tube DTI around resistor R2 rather than around the protective resistor R, an accidental short-circuit iny the tube will not short-circuit the protective resistor, thus adding to the safety of the circuit.

The transformer TI may have high leakage reactance, if desired, thus aiding the resistor R .in limiting the maximum current output of the apparatus. Since the vibrator V is well known, the structure of this vibrator has not been shown in detail. It will be understood that as long as the battery is connected across the vibrator, the contact fingers I3 and I4 will continue to operate, alternately closing the right-hand and left-hand As shown, the vibrator is connected to the battery B over'one-half of the winding II of transformer Tl, but this connection is not essential and the vibrator may be connected directly across the battery, if preferred.

The output of the apparatus of Fig. 1 is indicated diagrammatically in the voltage or current curve of Fig. 1a which is somewhat square-topped in form. v

Referring to Fig. 2, the apparatus of this figure provides a generally unidirectional output as in Fig. 1, which is periodically interrupted by a suitable vibrator or chopper device VI having a contact in the input circuit of the step-up transformer T2. The rate at which the contact I5 periodically opens and closes may be of the order of 40 to 60 times per minute and the on" period or length of time during which this contact remains closed in each cycle-may be adjusted to as short a time as is necessary to administer the desired shock. The periodic operation of the chopper VI serves to conserve power during the off intervals and also aids disengagement of the stock coming in contact with the charged conductor. In this figure, an independent source of direct current BI is' used for superimposing a unidirectional component on the alternating current shock impulses. 'Ihe transformer T2 supplies the shock potential through the resistors R and R2. The condenser C3 prevents the output winding of the transformer T2 from short-circuiting the battery BI but permits the alternating current output to pass freely therethrough.

The resistor R3 provides a means of adjusting the current flow from the battery BI.

Fig. 2a shows in anapproximate manner the nature of the voltage or current output delivered to the charged conductor by the apparatus of Fig. 2. The charge on the conductor is seen to alternate between a relatively high and a relatively low positive value, with the direct current bias effective between shock impulses.

Referring now to Fig. 3, this figure combines the apparatus of Fig. l which provides the unidirectional bias for weed destruction, with that portion of the apparatus of Fig. 2 which provides an`alternating current shock, and incorporates alarm apparatus which provides a warning when contact is established with the charged conductor. Since it is desirable to maintain the unidirectional bias effective for appreciable periods of time without interruption, the vibrator contact I5 is connected in the output rather than the input circuit of the transformer T3. In this manner, the shock potential which is impressed between conductor Ill and ground by windings I6 and I'I is intermittent in character, whereas the unidirectional bias which is impressed alternately by windings Il! and I8, throughlthe rectifying tube RT, is substantially constant. The resistor R6 limits the current in the shock circuit to a safe value, whereas the resistor R performs a similar function inthe circuit which supplies the bias potential.

The circuit of Fig, 3 is useful not only for keeping a charged enclosure free of grounds due to vegetation, but also provides a useful circuit for guarding an enclosure against. entry by burglars or other unauthorized persons. In order to provide an indication or alarm of contact with the charged conductor by such persons, we have provided novel alarm apparatus which includes a normally deenergized indication relay IR which controls a horn or howler H and which, in turn, is controlled by a reset push button PB. The relay IR is so designed as to pick up on the current from the tube RT flowing' through the charged conductor I0 when contact is established between this conductor and ground through the body of a person or otherwise.

The howler" H is normally short-circuited over the back contact 2I-22 of the relay IR and so is normally inoperative. When relay IR picks up, opening contact 2I-22, energy from the tube RT will flow through the condensers CS and C2, thus energizing the howler to provide the desired indication of contact with the charged conductor. Once relay IR picks up, a holding circuit for this relay becomes effective by yvirtue of the partial short-circuit which is established across the line through wires 24 and 25, front contact 2l-23 of relay IR, reset buttonl PB, and grounding resistor R5. Accordingly, relay IR will remain energized and the alarm will continue until such time as operation of the push button PB opens the holding circuit and restores the alarm apparatus to its normal inactive condition.

'Ihe purpose of condenser C2 is to improve the output of the rectifying tube. 'I'he condenser C6 permits the pulsating current in the output of the rectifying tube to be by-passed to the charged conductor I0 around the inductance due to the winding of relay IR which would otherwise imp'ede the flow of this current. Condenser C6 also completes the circuit to the how1er" H; when contact 2I-22 of relay IR is open.

The alarm apparatus shown in Fig. 3 may be incorporated into any of the other gures of the drawing when it isdesired to use the apparatus of these figures for protective purposes to prevent entry of a building or enclosure by unauthorized persons. v

The voltage or current which is effective inthe output circuit of Fig. 3 is shown diagrammatically in Fig. 3a.

Referring now to Figure 4, this figure shows one manner in which the weed-destroying appa- `ratus embodying our invention may be combined with a fence charger unit to provide the advantages of the apparatus shown in the previous figures, without the necessity for altering the fence charger unit itself or its internal connecktions in any way. The unit FC may be any suitable type of fence charger which delivers an a1- tied by the vibrator V, is impressed across the wires 8 and 9, as in Fig. 1, and is conducted to wire I0, on the one hand, over the resistors R and R4, and to ground, on the other hand, through the high tension terminali!! of the fence charger, the internal connections of the charger, and the ground terminal 20. One path for the output from the fence charger FC is from terminal I9, through wire 9, contact nger H of the vibrator V, one or the other half of the output winding l2 of transformer Tl, and wire 8, to the conductor l0. Since this output will usually be alternating or pulsating in character, it will also flow freely through the main path provided therefor which includes condenser C2, resistor R4, and conductor l0. The condensers C4 and C5 are used for the purposeof completing a bridge circuit together with the condenser C2 and a phantom condenser (not shown) which results from the inherent electrostatic capacity of the fence wire l to ground. -This capacity bridge is normally balanced so that the tube DT2 which is connected across the arms of the bridge is inactive, but lights up when the bridge is unbalanced due to a ground on wire l0 which tends to short-circuit the phantom condenser. Resistor R is the protective resistor, as in the remaining figures, and resistor R4 is provided for the purpose of limiting the discharge current from condenser C2 -is made variable in order that the bridge Amay be balanced for diiferent values of the capacity of wire I0 to ground, as may be required by individual installations.

Since it is only necessary to have the unidirectional potential applied at infrequent intervals for the purpose of destroying weeds coming in contact with the conductor I0, we have provided the switch S whichnormally disconnects the battery B from the circuit. Ihe discharge tube DT2 is providedl for the purpose of indicating when the weed growth, as indicated by a predetermined decrease in the .resistance of conductor l0 to ground is suflicient to render itnecessary to close the switch S and apply the unidirectional j potential. As long as the resistance of conductor I0 to ground is above the predetermined value, the condenser bridge will not be unbalanced sufflciently to-cause the discharge tube DT2 to glow.

When, however, the resistance of wire I0 to.

vunit FC may be of any suitable type and may deliver either an alternating or a direct current output, either steady or intermittent in character. If the output from the unit FC is alternating, it has been our experience that the weeds will not be effectively destroyed. The same is also true if the output is direct current but the charged conductor o1; fence is made negative with respect to ground. Moreover, even if the charged conductor is made positive, but if the potential is not properly chosen or is not applied for a prolonged time but is applied in intermittent irnpulse form, then it has been our experience that effective weed destruction will not be obtained. In view of the foregoing consideration, the advantages of the apparatus shown in Fig. 4 as well as of the remaining figures will become readily apparent.

The condensers C2,.C4, and C5 of Fig. 4 may have values of the order of-0.25, 0.1, and 0.01 microfarad, respectively. In Figs. 2, 3, and 4 in which a separate unidirectional potential is introduced for weed-destroying purposes, the value of this potential may be of the order of three or lfour hundred volts, and we have found it ordinarily suicient if this potential is maintained applied for a period of one or two days at a time. The actual potential appears less important than the current which should be of the order of one -to ve milliamperes for effective weed destruc- If the unidirectional potential is used for both weed destruction and stock control or'for other protective purposes as in Fig. 1, then the latter considerations determine the value .of the potential and the potential in these iigure is, as a matter of course, suiicient for weed 'destruction. If the fence charger FC inA Fig. 4 is of a type which is designed to deliver unidirectional impulses of negative polarity with respect to ground, then the charger should be so connected into the circuit that its positive terminal is connected with wire 9 and its negativeterminal is connected with ground.

It will be understood that the various values tus which is provided for stock herding or other protective purposes.

If the fence charger FCv is assumed to deliveralternating current impulses, then the charge on As soon as the vegetation the conductor l which is impressed by the apparatus of Fig, 4 is` somewhat similar to that shown diagrammatically in Fig. 3a. If the charger delivers unidirectional current impulses, then the resultant output will have a wave form similar to that indicated in the curve of Fig. 4a.

It will be understood that the apparatus of each of the Figs. 1 to 4, inclusive, may be used not onlyi'or weed destruction but also for the protection of property to prevent entry by unauthorized persons into a yard, building, or other protected area. When so used, the alarm apparatus of Fig. 3 may be adapted in an obvious manner to provide an alarm in the event that contact is established with the charged conductor.

It will be apparent from the foregoing description that we have provided electrical fence charging apparatus for preventing short-circuits by vegetation and preventing unauthorized entry or escape from an enclosure which is highly effective yet simple, reliable, and safe in its operation. When used as a fence charger for herding farm stock, the apparatus provides a combination which is comparatively free from the trouble and annoyance caused by grounds on the charged conductor.

Although we have herein shown and described only a few forms of apparatus embodying our invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of our invention.

Having thus described our invention, what we conducto;` and ground in a direction to render said conductor positive with respect to ground,

said unidirectional potential augmenting said shock potential and providing a bias voltage effective for destroying said vegetation.

2. Apparatus for electric fence fcharging and for preventing short-circuits on the fence conductor by vegetation coming in contact therewith comprising, in combination, a source of alternating current, a transformer having its input winding energized from said source, means including a condenser for impressing the output from said transformer across said conductor and ground for providing a shock potential on said conductor, and a source of direct current connected across said conductor and ground in a direction to render said conductor positive with respect to ground, the potential of said direct current source acting to augment said shock potential and to provide a bias voltage effective for destroying said vegetation, said condenser acting to prevent short-circuiting of said direct current source by the output winding of said transformer.

3. Apparatus for electric fence charging and for preventing short-circuits on the fence conductor by vegetation coming in contact therewith comprising, in combination, a source of direct current, a transformer, a vibrator, means including `said vibrator for periodically energizing the input winding of said transformer with current from said source and for rectifying the alternating current induced thereby in the output winding of said transformer, means for impressing the rectified output from said transformer across said conductor and ground ina direction to render said conductor positive with respect to ground, and a source of shock-potential'included vin the circuit of said conductor and ground in a direction to aid said rectiiied output.

4. Apparatus for electric fence charging and for preventing short-circuits on the fence conductor by vegetation coming in contact therewith comprising, in combination, a source of direct current, a transformer, a vibrator, means including said vibrator for periodically energizing the input winding of said transformer with current from said source and for rectifying the alternating current induced thereby in the output winding of said transformer, means for impressing the rectiiied output from said transformer across said conductor and ground, and a source of shock potential included in the circuit of said 'conductor and ground so as to superimpose said shock poten.

tial upon said rectified output.

5. Apparatus for electric fence charging and for preventing short-circuits on the fence conductor by vegetation coming in contact therewith comprising, in combination with said conductor, a source of direct current, a transformer, a vibrator, means including said vibrator for periodically energizing the input winding of said transformer with current from said source and for rectifying the alternating current induced thereby in the output winding of said transformer, means for impressing the rectified output from said transformer across said conductor and ground in a, direction to render said conductor positive with respect to ground, a source of shock potential included in the circuit of said conductor and ground so asto superimpose said shock potential uponsaid rectified output, a normally balanced capacity bridge including in one of its arms the distributed electrostatic capacity of said conductor to ground, and an indicator controlled by said bridge and effective for providing an indication when said bridge becomes unbalanced due to the occurrence of a, ground on said conductor.

6. Apparatus for electric fence charging and for preventing short-circuits on said fence by vegetation coming in contact therewith comprising, in combination, means including a rst source of current for impressing a shock potential between said fence and ground, and means including a separated effective second source of current for substantially constantly impressing a unidirectional potential between said fence and ground in a direction to render the fence positive with respect to ground, said unidirectional potential augmenting said shock potential and providing a bias voltage effective for destroying said vegetation.

rI. Apparatus for electric fence charging and for preventing short-circuits on said fence by vegetation coming in contactl therewith comprising, in combination, means, including a rst source of current for periodically impressing a shock potential between said fence and ground, and means including a separately effective second source of current for substantially constantly impressing a unidirectional potential between'said fence and ground in a direction to render the fence positive with respect to ground, said unidirectional potential providing a bias voltage effectivefor destroying said vegetation.

8. Apparatus for electric tence chemin! and for preventing short-circmts on said fence by vegeta.-

tion coming in contact therewith comprising, 1n

combination, means including-s rst source o! current for impressing s'shock potential between said fence and ground, and means including e separately eective source of current for substantially constantly impressing e unidirectional potentlsl between seid fence und ground in a direcnon u rende: me fence positive with respect to ground, seid unidirec tion.

NORMAN F. AGNEW. WILLARD P. PLACE.

tionel potentiel providing" g biss voltage effective for destroying seid vegeta- 

